INCLUSION OF SPIN-LABELED MOLECULES IN THE SOLID PHASE OF CYCLODEXTRINS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We prepared inclusion complexes of beta and gamma cyclodextrins (CD) with spin labeled compounds: several n-doxylstearic acids and esters/amides of C8 and C16 fatty acids with TEMPOL/TEMPAMINE and studied them by HF ESR at 170 GHz and X-Band. The spectra in CD crystallohydrate show patterns of fast near-ideal axial rotation, which is about Z-axis for doxylstearic acids and about X-axis for TEMPO derivatives. Dehydration of the crystallohydrate stops Z-rotation of doxystearic acids but has less effect on the dynamics of the X-rotating compounds. The spectra can be used at lectures and workshops as good illustrative examples for the effects of anisotropic motion in ESR and excellent orientation resolution of HF ESR. At HF, once motion is discernable in the spectrum, one can discern about which axis the motion occurs. A striking feature of molecular in the solid CD phase is detectable mobility at very low temperatures. HF ESR indicates averaging of the g-tensor values and, hence, molecular motion starting at 20K.